Field of the Invention
The present invention relates to a light source unit and a projector including this light source unit.
Description of the Related Art
In these days, data projectors are used on many occasions as image projection systems which project a screen of a personal computer or a screen of video equipment, as well as images based on image data stored on a memory card onto a screen. These projectors are such that light emitted from a light source is collected onto a micromirror display device called a digital micromirror device (DMD) or a liquid crystal panel, so that a color image is projected onto a screen for display thereon.
Conventionally, in the mainstream of these projectors, high-intensity discharge lamps have been used as a light source. In recent years, however, various types of projectors have been developed which use, as a light source, light emitting diodes, laser diodes, organic electroluminescence, or luminescent material.
Japanese Unexamined Patent Publication No. 2015-222299 discloses a projector having an excitation light source, a luminescent plate on which a luminescent material layer is provided, and a diffusing plate on which a plurality of diffusing zones having different diffusing angles are provided. The luminescent plate is a luminescent wheel and includes a zone which transmits or diffuse transmits excitation light from the excitation light source. This prevents the reduction of utilization efficiency of excitation light and allows excitation light to be diffuse transmitted at an appropriate diffusing angle even when the brightness of excitation light is adjusted to deal with a number of projection modes.
In addition, a projector disclosed by Japanese Unexamined Patent Publication No. 2012-128438 includes a first light source which emits laser light in the blue wavelength range, a color wheel, and a second light source which emits light in the red wavelength range. A luminescent material layer which emits light in the green wavelength range when receiving laser light as excitation light and a diffusing layer which diffuse transmits laser beam are provided end to end on the color wheel. A light source unit generates light source light in which light in the green wavelength range generated as a result of light in the blue wavelength range being emitted from the first light source and light in the red wavelength range from the second light source are mixed by partially overlapping a period during which light in the green wavelength range is emitted as a result of light in the blue wavelength range being emitted from the first light source and a period during which light in the red wavelength range is emitted from the second light source. This enables the light source unit of Japanese Unexamined Patent Publication No. 2015-222299 to deal with a desired color environment in relation to color balance, the brightness of a projected image and the like at all times.
In the projector disclosed by Japanese Unexamined Patent Publication No. 2015-222299 described above, the luminescent material layer and the zone which transmits or diffuse transmits excitation light are provided continuously in a circumferential direction on the luminescent plate. When the light source unit emits light in the blue wavelength range, the light in the blue wavelength range is incident on the zone where it is transmitted or diffuse transmitted, and when the light source unit emits light in the green wavelength range, the light in the green wavelength range is shone on to the luminescent material layer on the luminescent plate. Additionally, when a boundary portion between the zone where excitation light is transmitted or diffuse transmitted and the luminescent material layer is situated on an optical path of excitation light, the excitation light source does not emit excitation light. Due to this, in the projector disclosed by Japanese Unexamined Patent Publication No. 2015-222299, a period exists during which no light is emitted, resulting in a case where a projected image cannot be illuminated sufficiently.
In general, luminosity factors differ from wavelength to wavelength. For example, the luminosity factor of light in the red wavelength range is relatively lower than those of light in other wavelength ranges of colors. Consequently, in the case where it is desired that a highly bright image is projected by the use of the projector disclosed by Japanese Unexamined Patent Publication No. 2012-128438, it is necessary to enlarge the size and output of the red light source greater than those of the blue light source and the green light source which emit blue light and green light both having higher luminosity factors than that of red light to increase the luminance of the red light source. However, when the size and output of the light source which emits light having the lower luminosity factor are enlarged, there may be caused fears that the arrangement of constituent optical parts becomes inefficient or the luminous efficiency of the light source is lowered due to the heat value thereof being increased. In addition, in the case where the luminance of a wavelength component of the light source light which has a low luminosity factor is low, the extent to which the brightness and color balance of a projected image is adjusted becomes narrow.